I bought a 1990 3.0 300E (144k) three years ago that has been leaking oil for the past two years. I have pulled the powertrain from the vehicle (engine and transmission) so that I can refurbish the block and cylinder head (the prime source of the leaks). I know this is overkill, but I want to solve all the present and future oil leaks at once and insure the car runs well for my son for the next four or five years. Besides, I wasn't sure the rear main seal wasn't also leaking so why not go all the way. It only took another couple hour after I removed the cylinder head before I was ready to hoist the powertrain out.
But I now need to separate the engine from the trans so I can have the block cleaned and checked out.

I purchased the twin CD set for the car (W124) from mercedeshop.com but it doesn't contain the sections (26 or 27) that detail separating the engine from the transmission. I'm worried there are some components in the transmission that must not be allowed to become dis-engaged when I separate them. Anyone know where I can go to find this out?

I'd also like advice on how best to refurbish the engine and cylinder head.
I know where all the oil leaks are and already did the easy job of first replacing the valve cover gasket but there were two other leaks - the first I could easily see - the upper timing cover seal .

My mechanic visually surveyed the engine (externally) and also said the head gasket was leaking. I agreed since I also found small quantity of oil in the antifreeze when I drained the radiator. I don't mind doing the mechanical diassembly and re-assembly of major components to save the labor dollars but I'm unsure at what point I should start using a qualified mechanic. Can a do-it-yourselfer do a valve job? How about replacing bearing sets and pistons rings in the block itself? I would of course still have to send the block and head out to have them, cleaned and checked for straightness.

I don't want to dump too much money in the car since it is only used during the summer for my son to drive back and forth to his summer camp job. What is a reasonable set of tasks to do?

The car has been driving well - I didn't do a compression test before I started because I assumed I wouldn't get a good reading because of the head gasket.
Don't know for sure about rear main seal yet. Chances are all the oil I've found around the engine/transmission junction has simply been weeping down and then spraying all over the place.